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7/28/2019 Douglas Amato, Thesis.pptx
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Douglas Amato
Latent Cysteine Residues on
Polymers prepared via Freeand Controlled Radical
Polymerizations
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Part ILatent cysteine residues formed via RAFT
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Goals of Click Chemistry
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Quantitative yields
Tolerant to functional groups
Insensitive to solvents
Example:
Copper mediated azide alkyne cycloaddition
R+ R'
N3Cu(I) N
NN
R
R'
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Development of New Click Rxns
Variety of Click reactions currently exist
Diels-Alder (DA)
Thiol-ene/yne (TE/TY)
Oxime
Limitations
Require an external stimulus (DA & TE/TY)
Require additional reagents (TE/TY)
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Goal - Develop Click chemistry that is biocompatible, non-
reversible, and does not require an external stimulus to add
new functionality to existing materials
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Thiazolidine linkages
Reaction is simple
No external stimulus or additional reagents
Not thermally reversible
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Example of thiazolidine linkages
Grinstaff lab at BostonUniversity
Utilized as suturingmaterial in eyesurgery
Challenging sythesis
Limited through-put
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Reversible AdditionFragmentation Chain
Transfer (RAFT) Polymerization
Predetermined Mn
Low PDI
Able to prepare block copolymers
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RAFT
Wide range of monomers Terminated with transfer agent
Can reduce transfer agent to thiol functionality
Part of thiazolidine linkage
Need amine functionality8
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Thiazolidine Prepolymer
Prepare a styrene-block-acrylonitrile copolymer
Reduce to form a cysteine like functionality
Only need/want a few AN repeat units
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Polymer Synthesis
Simple and efficient synthesis
Able to prepare large quantities of material
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Step-Wise Reduction Method
Reduce and prepare disulfide to prevent coupling
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Coupling Experiments
Clean shift in GPC indicates simple and effective coupling12
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Limitations and Solutions
LAH : effective but incompatible with other functional groups
Use tetrabutylammonium borohydride (TBABH4)
New transfer agents Prepare easy to synthesize RAFT transfer agents
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New Transfer Agents
Simple and efficient synthesis
Able to polymerize styrenes and acrylates
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TA:1 Polymer Synthesis
Modification of previously established method New AN extension conditions
15Conditions : A) TA-1, RAFT; B) AN, RAFT; C) MTS, propyl amine;D) i TBABH4, THF, EtOH ii - DTT, isophthaldehyde
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Polystyrene
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PS-PAN
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PS-PAN-S-S-CH3
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Coupling
TA-1 and TA-3 showed best coupling, but not nearideal.
TA-1 used for optimization due ease of synthesis
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Potential Issues
Solvent
Reaction time
Dithiothreitol
Basic solution
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Solvent / Reaction Time
More polar= higher coupling
Time for thiazolidine ring formation insignificant
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Dithiothreitol
More DTT = higher coupling efficiency
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Potassium Carbonate
More K2CO3= Increase in coupling
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Conclusions / Future Work
Trithiocarbonates unable to achieve 100 % coupling
Coupling conditions were attempted to be optimized Dependent upon : [K2CO3],[DTT],solvent
New goal: synthesis of a single molecule that containscysteine residue to attach to polymer
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Part IILatent small molecule cysteine residues
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Goals
1. Design a molecule that contains a latent(i.e. protected) cysteine residue
2. Incorporate molecule into a polymer
3. Prove exposure of cysteine residues
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Initial synthetic scheme
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Synthesis of mesylated compound successful.
However required column to purify
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Mesylate to thioacetate
Showed multiple spots via TLC
Alternative route investigated
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New Approach
Start with cysteine and add protectinggroups
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Thia
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1H NMR
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a
a
b
b
c
c
d
d
Thia
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Next step
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Forma-thia
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1H NMR
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thia
Forma thia
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Alkylation of carboxyl group
Ester proved unstable in acid
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Solution
Use acid stable linkage such as amides
Various carbodiimides did not prove to beeffective
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Alternative to carbodiimide coupling
Mixed anhydride
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Proof of amide formation
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formathia
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Incorporation into Polymeric System
Need to synthesize polymerizable amines.
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Routes
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Synthesis of 4-vinylbenzyl amine:
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Synthesis of 4-vinylbenzyl amine
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a
a
a
a
a
a
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Ligate polymerizable amine
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?
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NMR
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Polymerization of protected molecule
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NMR
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Issues with deprotection
IR could not detect difference fromprotected vs. unprotected
Need higher amount of cysteine within thebackbone
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Alternative synthesis
First attach propargyl amine
Then click azide to alkyne
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NMR
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Evidence of reversibility
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Conclusion
Latent cysteine residues derived frompost-polymerization modification arepossible, yet are not fully optimized.
A facile, high yielding set of reactions havebeen found to produce a protectedcysteine
The deprotection of the cysteine has beenshown
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Future Work
Attach alkyne protected cysteine topolymers with pendant azides
Thiolene/yne chemistry with latent thiolresidue in RAFT
Creation of new materials with pendentcysteines.
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Acknowledgements
Advisor: Dr. Philip Costanzo
Thesis Committee:
Prof. Chad Immoos
Prof. Derek Gragson
Funding provided by an award from theResearch Corporation for Science
Advancement
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Costanzo Research Group
Dahlia Amato
Anton Chavez
Julia Dean
Guilhem Dehoe
Thaddeus Formal
Alex London
Tristan Kleine
Craig Machado
Miles Markmann
Leanna Monteleone
Chris Pattillo
Dimitri Pappademos
Alicia Ross
Kim Varney
Anthony Varni
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Polymers & Coatings Program
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Chemistry & Biochemistry Department
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Thank You